1. Field of the Invention
The present invention generally relates to the field of surgical stapling devices, and more particularly to a surgical stapling device for applying staples in a layer of tissue.
2. Description of Related Art
A generic surgical stapling device is marketed under the name “Leukoclip” by the firm Smith & Nephew Medical Ltd., Hull, Great Britain. The Leukoclip comprises a handle-shaped device body to which is pivotably attached a similarly handle-shaped triggering lever. The triggering lever is connected to a mechanism that engages in a housing part that can be slid onto the device body. In its lower area the slide-on housing part contains a linear staple magazine and in its upper part it has a slide element, referred to as the upper die, and a guide therefore.
In the staple magazine are stacked a plurality of staples, one behind each other, in a pre-application position. In the pre-application position each staple consists of a straight staple cross bar with staple feet bent laterally and substantially perpendicular thereto. The staple feet have pointed ends. The entire stack of staples is spring-loaded in the staple magazine so that the stack of staples is forced towards a staple outlet of the magazine. Each foremost staple in the stack of staples is positioned directly under the upper die. When the triggering lever is actuated, its mechanism pushes the upper die downwards, against spring pretension, towards the staple outlet. There, a groove in the front edge of the upper die and running parallel to the staple outlet, receives the staple cross bar of the foremost staple and transfers the foremost staple to an anvil below the staple outlet. The anvil consists of a metal tab that is fixed relative to the staple outlet and is oriented parallel and centrally to the staple cross bar, extending approximately over half the width of the staple cross bar. When the triggering element is further actuated, the staple crossbar is pressed by the front edge of the upper die against the anvil, while side areas of the upper die, which are movable relative to this front edge, fold downwards the two outer sections of the staple cross bar extending laterally beyond the anvil and thus bend the staple feet inwards. The folded areas between the staple feet and the remaining staple cross bar are referred to in this case as staple legs. When the Leukoclip is used as intended, the pointed staple feet penetrate into a layer of tissue and are secured in position when bent. In this way, the edges of a wound, for example, can be held in an abutting position to each other.
In order to support detachment of the applied staple from the Leukoclip stapling device, a “kick-off” mechanism is provided beneath the staple magazine. This mechanism takes the form of a flat metal tongue that extends to a point directly below the anvil. It can be displaced linearly and is spring-loaded against the direction of staple transport in the magazine. This means that in the relaxed state the front edge of the kick-off tongue is located behind the front edge of the anvil, while in the tensioned state both front edges are flush with one another. An extension of the kick-off tongue, designed as a separate push rod, extends through the rear wall of the slide-on device part so that in the assembled state of the Leukoclip stapling device, and with the triggering lever in the ready position, the kick-off tongue extension is displaced forwards against the spring pressure into the tensioned position by a corresponding shoulder on the triggering lever, i.e. the front edge of the tongue comes flush with the anvil.
When the triggering lever is actuated, the kick-off tongue extension is released, the tensioning spring relaxes and the kick-off tongue is displaced rearwards as the staple is being applied. Only when the triggering lever has been released, i.e. it has returned to its ready position after application of the staple, does the kick-off tongue return to its tensioned position, in which it exerts pressure from behind with its front edge against the folded staple legs and thus actively detaches the applied staple from the anvil.
What is disadvantageous in this known stapling device is the fact that a large degree of mechanical effort must be put into the design of the kick-off mechanism. In order to tension the spring against the staple transport direction a spiral spring must be used as an additional component, and at least one rigid projection passing through the tongue must be created as an abutment for the spiral spring, so that the direction of the spring tension can be reversed. In addition, in the Leukoclip the tongue extension takes the form of a separate push rod, which requires the use of an additional component with corresponding manufacturing and assembly costs.
EP 0 864 297 A2 and the parallel U.S. Pat. No. 5,908,149 A describe a surgical stapling device that is commercially available under the name “Proximate Plus MD” and has a simplified kick-off mechanism. In this stapling device, a kick-off tongue is arranged beneath the anvil and its front area can be bent elastically downwards. When the staple is applied, the folding of the staple legs, which interact with the rounded end areas of the front edge of the kick-off tongue, cause the front area of the tongue to bend elastically downwards. When the triggering lever is returned to its ready position, the downward-bent front area of the tongue snaps back into its starting position at the moment when the guiding groove of the upper die releases the staple cross bar and, as it moves upwards, comes into contact with the rear surfaces of the bent staple legs, thereby pushing the entire staple off the anvil.
One disadvantage of this device is the rapid wear that occurs to the plastic kick-off tongue, in particular in the lateral end areas of the front edge of the tongue, which are particularly important for the action and which are heavily stressed when the device is actuated. Even slight wear in this area results in the tip of the tongue no longer being sufficiently bent downwards and the ejection force is correspondingly reduced when the tip snaps back. Another disadvantage of this device is that when the kick-off tongue is bent downwards, it can come into contact with the tissue to be stapled and this can give rise to undesired contamination.